Vinyl ester resins and unsaturated polyester resins are industrially important in the manufacture of reinforced plastic components, boat hulls, fireproof molded articles, linings, paints, coating compositions, tanks, vessels, scrubbers, smoke stacks, pipe linings and other composite materials. Where superior toughness and corrosion resistance is desired, the more resistant vinyl ester resins are generally employed. These resins are generally prepared and mixed with a polymerizable monomer such as styrene, in order to reduce their viscosity. When cured, the styrene becomes a part of the resin system to produce a rigid cross-linked structure with desirable properties.
The presence of large amounts of styrene in such resin compositions results in the emission of styrene vapors into the work atmosphere, which constitutes a hazard to workers. In view of this workplace hazard, certain threshold concentration limits for styrene vapor have been established in many countries. Several methods of reducing styrene emission are described in the literature. One such method, described by Nylander in U.S. Pat. No 4,201,826, includes the addition of a film-forming material, such as a paraffin or hydrocarbon wax, to resin compositions in order to inhibit the vaporization of styrene. Paraffin or hydrocarbon waxes tend to migrate to the surface of the resin and serve as a film barrier which confine the styrene monomer within the resin.
While such systems successfully suppress the volatilization of styrene from the work atmosphere, laminates so prepared are deficient in their secondary bonding characteristics. For example, applications in which relatively thick reinforced plastic articles are produced, are generally prepared in several laminate passes with successive curings. Thus, one or more impregnated reinforced layers is applied and allowed to cure, followed by another series of applied reinforced layers, with further curing, etc. It is necessary that each successive layer forms a tight bond to the preceding layer. Paraffin and hydrocarbon waxes form surface films which are extremely useful in controlling styrene emissions. However, the wax surface films they produce effectively reduce adhesion. Therefore, it is not too surprising that they also impart a substantial loss in adhesive properties of the resin to the reinforcing medium, as well as to secondary bonds formed by multiple-pass laminations.
Various adhesion promoters are known to the art which improve the adhesion of resin mixtures to reinforcing medium, as well as to resin laminates themselves, as in the case of multi-pass laminates. In general, however, these adhesion promoters are only partially soluble in styrene containing resin compositions, and soon separate upon standing to form bi-phasic mixtures. Accordingly, in many instances, adhesion promoters are added just prior to using the resin mixtures, in order to avoid their separating and floating to the top of the resin composition. It would be highly advantageous to be able to provide a complete resin system, containing the resin, styrene wax and adhesion promoter, which has a low styrene emission, and which will not separate on standing.